In an information recording device such as a magnetic disk drive or an optical disk device that records and reproduces information to and from a disk that rotates, vibration in the disk causes a deviation in position between the head for recording and reproducing information and the track which is a place where information is recorded on the disk, and has, therefore, been desired to be decreased. In recent years, in particular, the positioning maintaining a high precision has been requested along with an increase in the recording density, and it is becoming more important to decrease vibration in the disk caused by the disturbance in the flow of air in the device, which is called disk fluttering, accompanying an increase in the rotational speed of the disk.
A conventional magnetic disk drive has been disclosed in, for example, JP-A-11-232866 (patent document 1). The magnetic disk drive of the patent document 1 includes a rotary magnetic disk, a head for recording or reproducing information into or from the magnetic disk, and a head support mechanism for supporting the head, wherein a shroud is provided surrounding the outer circumference of the magnetic disk except a portion where a carriage arm linked to the head support mechanism is inserted, and a gap between the outer circumferential edge of the magnetic disk and the shroud surface is selected to be not smaller than 0.1 mm but not larger than 0.6 mm. There has been described that the above constitution eliminates a difference in the air pressure occurring on both surfaces (front and back surfaces) of the disk and, as a result, decreases the fluttering.
A conventional disk flutter-suppressing device has been disclosed in, for example, JP-A-2000-331460 (patent document 2). The disk flutter-suppressing device of the patent document 2 includes a disk spindle mechanism having one or a plurality of disks, wherein squeeze air bearing plates having a partial annular flat surface expanding in the circumferential direction and in the radial direction, are fixed onto the uppermost surface, onto the lowermost surface, or onto both disk surfaces, or onto the surfaces on one side of all disks facing the disk surfaces maintaining a gap of not larger than 0.3 mm. There has been described that the above constitution is effective in suppressing the disk fluttering owing to the damping effect of the squeeze air films.
Furthermore, conventional slit shrouds have been disclosed in, for example, JP-A-2000-228079 (patent document 3) and JP-A-2004-234784 (patent document 4).
In the magnetic disk drive of the above patent document 1, however, the outer circumferential edge of the magnetic disk is brought close to the whole shroud surface. At the time of incorporating the magnetic disk, therefore, the outer circumferential edge of the magnetic disk is likely to come into collision with the shroud surface leaving a problem from the standpoint of incorporating the magnetic disk.
In the disk flutter-suppressing device of the above patent document 2, the squeeze air bearing plates are brought close to the recording surface of the magnetic disk and are, therefore, likely to come in contact with the recording surface of the magnetic disk. In case they come in contact, the recording surface is damaged arousing a problem concerning reliability in the recording. In the slit shroud of the above patent documents 3 and 4, a gap between the disk and the slit shroud is uniform and the slit shroud is opened at a side which does not face the disk.
When a portion is specified for suppressing the vibration of the rotary disk, the portion where vibration is to be suppressed may be effectively handled. In information recording units such as a magnetic disk drive and an optical disk drive, it is becoming necessary to accomplish the positioning highly precisely on a track of a high recording density, and it is particularly important to lower the amplitude of vibration at the head position.